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Chapter 5: Problem 10

Does \(\Delta H_{\mathrm{rxn}}\) for the reaction represented by the following equation equal the standard enthalpy of formation for \(\mathrm{CH}_{3} \mathrm{OH}(l) ?\) Why or why not? [Section 5.7] $$ \mathrm{C}(\text { graphite })+4 \mathrm{H}(\mathrm{g})+\mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l) $$

Short Answer

Expert verified
No, the enthalpy change of the given reaction (螖Hrxn) does not equal the standard enthalpy of formation for CH鈧僌H (liquid) because the elements on the reactant side are not in their standard states, specifically Hydrogen and Oxygen have different forms (H鈧�(g) and O鈧�(g)) in the standard enthalpy of formation definition.

Step by step solution

01

Write down the definition of the standard enthalpy of formation for CH3OH(l)

The standard enthalpy of formation for CH鈧僌H is the enthalpy change that occurs when 1 mole of CH鈧僌H (liquid) is formed from its elements in their standard states. The reaction can be represented by the following equation:$$ \mathrm{C}(\text { graphite })+\frac{2}{1}\mathrm{H}_{2}(\mathrm{g})+\frac{1}{2}\mathrm{O}_{2}(\mathrm{g})\longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l) $$
02

Compare the given reaction to the standard enthalpy of formation definition for CH3OH(l)

Now, we compare the given reaction:$$ \mathrm{C}(\text { graphite })+4 \mathrm{H}(\mathrm{g})+\mathrm{O}(\mathrm{g})\longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l) $$with the standard enthalpy of formation definition:$$ \mathrm{C}(\text { graphite })+\frac{2}{1}\mathrm{H}_{2}(\mathrm{g})+\frac{1}{2}\mathrm{O}_{2}(\mathrm{g})\longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l) $$
03

Determine if 螖Hrxn for the given reaction equals the standard enthalpy of formation for CH3OH(l)

Upon comparing the two reactions, we can see that they are not identical, mainly because the types of Hydrogen and Oxygen in the given reaction are not in their standard states (H鈧�(g) and O鈧�(g)). Consequently, the enthalpy change of the given reaction (螖Hrxn) does not equal the standard enthalpy of formation for CH鈧僌H (liquid). Answer: No, the enthalpy change of the given reaction (螖Hrxn) does not equal the standard enthalpy of formation for CH鈧僌H (liquid) because the elements on the reactant side are not in their standard states, as required for the standard enthalpy of formation definition.

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Most popular questions from this chapter

(a) Why are tables of standard enthalpies of formation so useful? (b) What is the value of the standard enthalpy of formation of an element in its most stable form? (c) Write the chemical equation for the reaction whose enthalpy change is the standard enthalpy of formation of glucose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{~s}), \Delta \mathrm{H}_{f}^{\circ}\left[\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right]\).

An aluminum can of a soft drink is placed in a freezer. Later, you find that the can is split open and its contents frozen. Work was done on the can in splitting it open. Where did the energy for this work come from?

The sun supplies about \(1.0\) kilowatt of energy for each square meter of surface area \(\left(1.0 \mathrm{~kW} / \mathrm{m}^{2}\right.\), where a watt \(=1 \mathrm{~J} / \mathrm{s})\). Plants produce the equivalent of about \(0.20 \mathrm{~g}\) of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) per hour per square meter. Assuming that the sucrose is produced as follows, calculate the percentage of sunlight used to produce sucrose. $$ \begin{aligned} 12 \mathrm{CO}_{2}(g)+11 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+12 \mathrm{O}_{2}(g) \\ \Delta H &=5645 \mathrm{~kJ} \end{aligned} $$

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(a) What is the kinetic energy in joules of an \(850-\mathrm{lb}\) motorcycle moving at \(66 \mathrm{mph} ?\) (b) By what factor will the kinetic energy change if the speed of the motorcycle is decreased to \(33 \mathrm{mph} ?\) (c) Where does the kinetic energy of the motorcycle go when the rider brakes to a stop?
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